1. Field of the Invention
The present invention relates generally to a hydraulic elevator system having an elevator car conveyed along a vertical shaft by hydraulic actuator means in which the hydraulic actuator means are located laterally with respect to the elevator shaft.
More specifically, the invention provides an elevator system with compensative means for balancing while concentrating the elevator car weight, by generating a compensating force corresponding to a specific lifting force.
2. Description of Related Art
In hydraulic elevator systems employing the method of concentrated car suspension in actual use, a single lifting cylinder placed centrally below the elevator car or two laterally lifting cylinders are used. In addition, there are many hydraulic elevator systems which have implemented the concentrated car suspension method by using various rope and balance arrangements. These systems have not been manufactured because of their complexity and high production costs. The systems employing one cylinder placed centrally below the elevator car are too expensive to be carried out because of the "well" required to install the lifting cylinder. In the systems using two cylinders, concentrated car suspension is obtained at high expenses (e.g. for the same lifting power, the expenses for two cylinders are bigger than the expenses for one cylinder). Furthermore, a wider elevator shaft is needed for the two cylinder solution and, additionally, due to the buckling effect, the maximum lifting height is decreased.
For the reasons stated above, most hydraulic elevators in use employ a lateral lifting method despite the high strain on the guide rails due to the unconcentrated car suspension. In these systems, the friction between the guide rails and the elevator car reduces the efficiency of the elevator as well as the travelling comfort. Furthermore, the guide rails have to be substantially heavier than in the case of elevators with concentrated car suspension. Moreover, the guide rails are subject to fast wear.
In order to overcome these problems, some of the hydraulic elevators employing a lateral lifting method in actual use are provided with a compensating rope for obtaining a concentrated car suspension. Thus, the "well" for accommodating the lifting cylinder is eliminated. Additionally, such systems require considerably less components and installation work than the two-cylinder systems. An elevator employing the lateral lifting method and provided with a compensating rope does not require as wide a shaft as needed for accommodating two cylinders placed on opposite sides of the shaft. Moreover, when a single cylinder is used, the frictional force is lower than in the case of two smaller cylinders. A greater effective lifting height is obtained as well.
Swiss patent CH 517,043 discloses a method for implementing concentrated car suspension for a hydraulic elevator employing the lateral lifting principle. In this patent the compensator between the lifting rope and the compensating rope consists of a lever balance hinged on the bottom of the elevator car and provided with rope pulleys at its ends. The lever balance dimensions depend upon the dimensions of the elevator car and thus the resulting device is always quite big (its width is at least equal to that of the car). The state of the balance must be continuously monitored via the car cable, using a suitable sensor or switch.
The teachings of the aforesaid prior art, require that the lifting rope, the compensating rope and the balance with its hinge and pulleys be located in the same plane as the car centre of gravity. However, in the present invention, the lifting rope and the centre of gravity of the car are located in one plane and the compensating rope and its pulleys are located in a plane parallel with the first one. This arrangement provides more freedom at the designing stage thus allowing better constructions to be achieved.
Furthermore, the present invention offers several advantages over the known systems. Since the lever balance is placed below or beside the lifting cylinder, it can be of reduced dimensions (about the size of the lifting rope pulley). In other words, the size of the balance is independent of the size of the elevator car. The pulleys for the compensating rope are mounted directly on the car frame without balances or hinges, thus avoiding an increase in the weight of the car. Since the balance is not mounted on the car but in the elevator shaft, it can be monitored easier (i.e. not via the car cable).